CVE-2019-20053 in UPX
Summary
by MITRE
An invalid memory address dereference was discovered in the canUnpack function in p_mach.cpp in UPX 3.95 via a crafted Mach-O file.
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Analysis
by VulDB Data Team • 04/11/2025
The vulnerability identified as CVE-2019-20053 represents a critical memory safety issue within the UPX (Ultimate Packer for eXecutables) compression utility version 3.95. This flaw exists in the p_mach.cpp source file within the canUnpack function, which is responsible for handling Mach-O binary formats commonly used on macOS and iOS systems. The vulnerability manifests when processing specially crafted Mach-O files that contain malformed memory references, leading to potential system instability or exploitation opportunities.
The technical nature of this vulnerability stems from an invalid memory address dereference condition that occurs during the unpacking process of compressed executables. When UPX attempts to decompress a maliciously constructed Mach-O file, the canUnpack function fails to properly validate memory pointers before accessing them, resulting in a segmentation fault or memory access violation. This type of flaw falls under the CWE-476 category of NULL Pointer Dereference, though specifically manifests as an invalid memory address dereference that can be triggered through crafted input rather than simple null pointer access. The vulnerability represents a classic example of improper input validation in binary decompression utilities that handle complex file formats.
The operational impact of CVE-2019-20053 extends beyond simple application crashes, as it could potentially be exploited to execute arbitrary code on systems running vulnerable versions of UPX. Attackers could craft malicious Mach-O files that, when processed by UPX for decompression, would trigger the memory access violation and potentially allow for privilege escalation or remote code execution depending on the execution context. This vulnerability affects systems that rely on UPX for executable compression and decompression, particularly those running macOS or iOS environments where Mach-O binaries are prevalent. The attack surface includes developers who use UPX for code distribution, system administrators managing compressed executables, and any environment where UPX is employed to handle binary files from untrusted sources.
Mitigation strategies for CVE-2019-20053 should prioritize immediate software updates to versions of UPX that have patched this vulnerability, as the original 3.95 release contains the flaw. System administrators should implement strict input validation procedures for all executable files processed through UPX, particularly those originating from untrusted sources. Additionally, organizations should consider implementing sandboxing mechanisms when processing compressed binaries to contain potential exploitation attempts. The vulnerability aligns with ATT&CK technique T1059.007 for execution through Mach-O binaries and represents a common vector for initial access through malicious compressed payloads. Security monitoring should include detection of abnormal memory access patterns and segmentation faults during decompression operations, with particular attention to systems where UPX is actively used for binary processing and distribution.